Comparative research on the evolution of parental care has followed a general trend in recent years, with researchers gathering data on clutch size or egg size and correlating these traits with ecological variables across a phylogeny. The goal of these studies is to shed light on how and why certain strategies evolve. However, results vary across studies, and we rarely have results explaining why the observed pattern occurred, leaving us with further hypotheses to test. By using a combination of comparative methods, we provide an explanation of how such patterns emerge based on the evolutionary timeline of constructing burrows and the energy invested into egg size and egg number; this combination also allowed us to pinpoint why the pattern occurred. We do so with data on freshwater crayfish, which are ideal for such investigations because they vary in their reliance on burrows, their body size, and their investment into their offspring. Specifically, we tested whether a strong dependence on burrows is related to investment in eggs (i.e., larger eggs or more eggs) given the body size of the species. Surprisingly, we found no correlation between burrowing and the size or number of eggs crayfish lay; instead, body size was the best predictor of the number of eggs (but not the size of eggs) that each species lays. Interestingly, our analysis suggests that crayfish ancestors had a small clutch size, relatively large eggs, and a weak connection to burrows. Thus, the shift to heavily relying on burrows appeared after this lineage was already investing in large eggs, which gives insights into the colonization of freshwater by an ancestral astacidean ancestor. While other studies show that the evolution of parental care strategies is not straightforward, our study provides a clear evolutionary timeline of the interplay between the evolution of burrowing behavior and shifts in the evolution of egg investment. Furthermore, our work showcases how merging multiple phylogenetically informed approaches can disentangle the origin and evolution of life history traits.

中文翻译：

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进化时间线有助于解释父母照顾策略的演变


近年来，关于父母照顾演变的比较研究遵循了普遍趋势，研究人员收集了有关窝大小或鸡蛋大小的数据，并将这些特征与整个系统发育中的生态变量相关联。这些研究的目的是阐明某些策略如何以及为何演变。然而，结果因研究而异，我们很少有结果来解释观察到的模式发生的原因，这给我们留下了进一步的假设来检验。通过使用比较方法的组合，我们根据建造洞穴的进化时间表以及投入到卵大小和卵数上的能量来解释这种模式是如何出现的;这种组合还使我们能够确定模式发生的原因。我们利用淡水小龙虾的数据来做这件事，这些数据是此类调查的理想选择，因为它们对洞穴的依赖、体型和对后代的投资各不相同。具体来说，我们测试了鉴于物种的体型，对洞穴的强烈依赖是否与对鸡蛋的投资（即更大的鸡蛋或更多的鸡蛋）有关。令人惊讶的是，我们发现挖洞与小龙虾产卵的大小或数量之间没有相关性;相反，体型是每个物种产卵数量（而不是卵的大小）的最佳预测指标。有趣的是，我们的分析表明，小龙虾的祖先的窝小，卵相对较大，并且与洞穴的联系较弱。因此，在这个谱系已经投资于大鸡蛋之后，出现了严重依赖洞穴的转变，这让我们了解了祖先 astacidean 祖先在淡水中的定植。 虽然其他研究表明父母照顾策略的演变并不简单，但我们的研究提供了一个清晰的进化时间表，说明了穴居行为的演变与卵子投资演变的变化之间的相互作用。此外，我们的工作展示了合并多种系统发育信息方法可以解开生活史特征的起源和进化。